Phosphorylation reactions by protein kinase A (PKA) are balanced by dephosphorylation reactions of protein phosphatases (PP) -1 and -2A. During the current period of support, the applicant showed that PKA stimulates the invasiveness of Lewis lung carcinoma (LLC) cells. The hypothesis of the present study is that the balance between PKA and PP-1/2A regulates tumor metastasis. The rationale for this hypothesis is their demonstration that metastatic LLC clones have a deficiency in PP-2A activity and upregulated PKA, and that nonmetastatic LLC cells acquire metastatic properties when PKA activity is elevated by blocking PP-1/2A. When PKA activity is reduced, or when PP-2A activity is increased, metastatic LLC become less invasive. This study will ask if the capacity of tumor cells to metastasize can be reduced by upregulating the activities of PP-1/2A and, in turn, reversing the metastasis-stimulatory effects of PKA. The Specific Aims that will test this hypothesis are: (i) To define the mechanisms that result in a deficiency in PP-2A activity in metastatic LLC cells and to determine if deficiencies in PP-2A occur in metastatic cells of other tumor types; (ii) To upregulate PP-1/2A activities in metastatic LLC and in primary human lung cancer cultures so as to reverse the metastasis-stimulatory effects of PKA; and (iii) To reduce LLC cell invasion and metastasis in vivo by upregulating PP-2A levels, and to determine if PP-1 can also contribute to the reversal of PKA-stimulated metastasis. Upon completion, these studies will have determined if elevating either PP-1 or PP-2A activities in tumor cells shifts the balance between PKA and PP-1/2A to reduce the metastatic properties of tumor cells. These studies will also have determined if strategies to elevate PP-2A activity of tumor cells in vivo block metastasis.